1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling the temperature of a reforming reaction catalyst for use with a power generator system that includes a fuel cell, in which a material for reforming such as methane, methanol, naphtha, and the like passes through a reformer which produces hydrogen gas from any of the material for reforming so as to be supplied to the fuel cell.
2. Description of the Prior Art
A conventional apparatus for controlling the temperature of a reforming reaction catalyst has an arrangement such as that shown in FIG. 1, and is specifically designed to control the rate of any material for reforming and combustion air to be supplied, thereby controlling the temperature of the reforming reaction catalyst.
Referring to FIG. 1, a reformer 1 accepts any material for reforming such as the one composed of a mixture of methanol and water, which will have passed through a material for reforming delivery pump 2 that delivers it to the reformer 1. The reformer 1 produces hydrogen gas by causing the reforming reaction. When hydrogen gas is produced, it is supplied to a fuel cell (FC) 3. Then, the FC3 produces a direct current (DC) power to be supplied to a transforming device 4 which usually has the form of an inverter. The transforming device 4 converts the DC power into an alternating current (AC) power to be supplied to any particular load 5.
The reforming process for the material for reforming consists usually of raising the temperature of any suitable reforming reaction catalyst 6 such as an alloy of Fe and Cu up to a certain value, followed by feeding the material for reforming into the reformer 1. The reforming reaction catalyst 6, which is usually provided in the granular forms, is filled in a reforming tube 7 which usually has the form of a hollow cylindrical pipe. The reforming reaction catalyst 6 is heated by the burner 8 through a heating medium such as oil. That portion of the material for reforming which has been produced as non-reaction reforming gas within FC3 is fed as off-gas fuel to the burner 8. The combustion air is fed through its blower 9 to the burner 8.
The temperature that occurs during the reforming reaction within the reformer 1, that is, the temperature of the reforming reaction catalyst 6, is sensed by a temperature sensor 11 which usually has the form of a thermocouple.
A signal 101 which represents the temperature as sensed by the sensor 11 is compared with the specific temperature value preset by a temperature setter 12 in the form of a variable resister, and any deviation of the temperature signal from the temperature setting is determined. If the temperature as sensed by the temperature sensor 11 is below the temperature setting, a signal 102 that represents the above deviation is inputted to a temperature regulator (CT.sub.1) 13 where it is amplified.
The FC3 provides its output current which corresponds to the value of the load 5, and this FC output current may be detected by a current detector (14) usually in the form of a current transformer. A signal 103 that is indicative of the current as detected is inputted to a load regulator (CT.sub.2) 15 in the form of an amplifier where it is amplified. The load regulator 15 changes the output current from the FC3 to provided the corresponding current that can affect the rate of the material for reforming and combustion air to be supplied. The output current from the FC3 increases with the increasing value of the loads, but as the reforming reaction, is the endothermic reaction, the temperature of the reforming reaction catalyst 6 lowers.
An output signal 104 that is outputted from the temperature regulator 13 and whose value has been amplified, and an output signal 105 that is outputted from the load regulator 15 and whose value has been amplified are inputted to a material delivery pump (CT.sub.3) controller 16 and to a combustion air blower (CT.sub.4) controller 17, respectively, both controllers usually having the form of a chopper. Each of those controllers 16 and 17 may control its respective voltage variably to be applied across a respective DC motor associated with the pump 2 and blower 9. The output voltages of the controllers may influence the number of revolutions for the respective DC motors so that the associated pump 2 and blower 9 can provide the appropriate amounts of material for reforming and combustion air to the reformer 1. That is, when the condition of the load 5 changes and the temperature of the reforming reaction catalyst 6 changes, the rates of the material for reforming and combustion air to be supplied are changed accordingly, respectively, keeping the temperature of the reforming reaction catalyst 6 at the constant value.
The whole control of the fuel cell power generator system is provided by a control program, which is stored in a memory located within a central controller which is not shown. Specifically, the temperature regulator 13, load regulator 15, material delivery pump controller 16 and combustion air blower controller 17 may be operated under control of the central controller or its control program.
Another conventional control apparatus, shown in FIG. 2, which also allows the temperature of a reforming reaction catalyst to be controlled is designed to control the temperature of the reforming reaction catalyst by controlling the rate of a promoter fuel and the rate of a combustion air variably. In FIG. 2, those locations which are similar to those in FIG. 1 are given the same reference numerals. Reference numeral 10 represents promoter fuel delivery pump which may be operated if the amount of the off-gas to be supplied from FC3 to the burner 8 is not enough to satisfy the specific combustion requirements, and will provide an additional amount of fuel.
The signal 104 outputted from the temperature regulator 13 is inputted to the promoter fuel delivery pump 10 and to the combustion air blower controller 17. The signal outputted from the load regulator 15 is inputted to the material for reforming delivery pump controller 16 and to the combustion air blower controller 17.
The amount of the material for reforming that will be supplied to the reformer 1 through the material for reforming delivery pump 2 is controlled by the for the material for reforming delivery pump controller 16 in response to the signal 105.
The DC motor associated with the promoter fuel delivery pump 10 may provide a variable number of revolutions in response to the signal 104, and the amount of fuel to be added to the reforming burner 8 through the pump 10 may be determined as appropriate, depending upon the particular number of revolutions.
The amount of air to be supplied to the reforming burner 8 through the combustion air blower 9 may be controlled by the combustion air blower controller 17 which responds to the signal 104 or 105. The combustion air that will be supplied to the reforming burner 8 may be adjusted to the amount of promoter fuel that is to be supplied in response to any changes in the reforming reaction catalyst temperature. In this way, the reforming reaction catalyst 6 may be kept to its constant temperature.
It may be appreciated from FIG. 1 that if the FC3 should provide output that can meet the particular power requirements for the load 5, the reformer 1 must produce the amount of hydrogen gas sufficient to satisfy those requirements. That is, whether the amount of material for reforming to be supplied is to be increased or decreased may essentially depend upon the output current value of the fuel cell.
As described earlier, the catalytic reaction that occurs within the reformer 1 is the endothermic reaction, the temperature of the reforming reaction catalyst 6 falls as the catalytic reaction progresses. This may be explained by using FIGS. 3A, 3B and 3C.
In FIG. 3A, the pump 2 is operated to deliver the amount of a material for reforming that can meet the particular power requirements of the load 5 into the reforming tube 7 within the reformer 1 on its inlet. Then, the catalytic reaction occurs between the reforming reaction catalyst 6 and the material for reforming. As this catalytic reaction progresses, it produces hydrogen gas which goes out of the reforming tube 7 on its outlet. Under the initial light load condition, that is, when the amount of the material for reforming to be supplied to the reformer 1 is small, the catalytic reaction will occur near the point A. Subsequently, as the load 5 is increasing, the amount of the material for reforming to be supplied to the reformer 1 is increasing accordingly. Then, the reaction will occur between all of the reforming reaction catalyst 6 and the increased amount of the material for reforming throughout the reforming tube 7.
As it may be seen from FIG. 3B, therefore, the temperatures T.sub.A, T.sub.B and T.sub.C of the reforming reaction catalyst 6 which appear at the different points A, B and C are changing in response to the variations in the load condition. The curves which are identified by reference numerals 25, 50, 75 and 100 in FIG. 3B explain the relationships between the locations where the reaction occurs throughout the reforming tube 7 and the corresponding changes in the temperature, when the load 5 is placed at 25%, 50%, 75% and 100% of its rated value, respectively. Again, as described earlier, the reforming reaction is the endothermic reaction, temperature of the reforming reaction catalyst 6 decreases gradually as the load 5 is increasing.
How the temperatures at the points A, B and C change under the different load conditions is shown in FIG. 3C. At the point A which is located the nearest to the burner 8, the temperature of the reforming reaction catalyst 6 is rising under the light load condition, and is falling as the reforming reaction progresses under the heavy load condition. A relatively great change in the temperature may be noticed. As the reforming reaction is gradually going down through the reforming tube 7, beginning with the point A through the point B and ending with the point C, the change in the temperature of the reforming reaction catalyst 6 that may be caused by the load 5 tends to become smaller.
As the catalytic reaction which occurs within the reformer 1 is accompanied by the endothermic reaction, the temperature of the reforming reaction catalyst 6 may have the greater reduction as the load 5 is placed under the heavier condition. In this respect, the conventional temperature control method, whereby the control is only provided to ensure that the catalyst 6 is kept to its constant temperature under the different load conditions, has the problems which may be listed as follows:
(1) Because of a drop in the temperature of the catalyst that occurs during the reforming reaction process, an additional amount of the material for reforming must be added into the reformer 1 in order to keep the temperature constant. Unless any additional material for reforming is added, the catalyst will have its temperature falling gradually along the curve P shown in FIG. 4. As the material for reforming to be added in increasing, the produced off-gas is also increasing with the result that the amount of combustion air to be added must also be increased as seen from FIG. 4. This may degrade the running efficiency of the plant facilities.
(2) As it may be seen from FIG. 4, if the amount of material for reforming to be added is to be increased further as noted in (1) described above, in an attempt to keep the catalyst temperature constant, it may cause a further drop in the catalyst temperature. In the positive feedback control, oscillations may be produced as explained by the principle of the feedback control. Those oscillations may make the temperature control for the reforming reaction catalyst 6 unstable and unreliable, and the catalyst temperature may have a great change which may degrade the catalyst's performance.
(3) When the load 5 is decreasing, the burner 8 will have been supplying a great deal of combustion heat until the moment when the load 5 has actually decreased. In such case, the catalyst temperature will overshoot, which may possible cause the degradation in the catalyst performance, or shorten its life. This is also seen in FIG. 4.
(4) The reforming reaction catalyst 6 has a very large time constant (such as between several minutes and several ten minutes) when its temperature is changing, and a great difference in the temperature is also noticed at the points A, B and C shown in FIG. 3A. Specifically, the temperature may change more rapidly in the area which is located nearer to the point A, whereas it may change more slowly in the area located nearer to the point C. Any attempt to keep the catalyst temperature constant under those circumstances might fail because there is a timing delay in detecting any change in the catalyst temperature. Thus, the temperature control cannot be achieved with high precision.